Circuit switchable optical device

ABSTRACT

A circuit switched optical device includes a first array of intersecting hollow waveguides formed in a first plane of a substrate. A second array of intersecting hollow waveguides is formed in a second plane of the substrate, and the second plane is positioned parallel to the first plane. An optical element within the first array selectively redirects an optical signal from the first array to the second array.

BACKGROUND

As computer chip speeds on circuit boards increase to ever fasterspeeds, a communications bottleneck in inter-chip communication isbecoming an increasing concern. One solution may be to use fiber opticsto interconnect high speed computer chips. However, most circuit boardsinvolve many layers and often involve tolerances in their manufacture ofless than a micron. Physically placing fiber optics and connecting thefibers to the chips can be too inaccurate and time consuming to bewidely adopted in circuit board manufacturing processes. Furthermore,routing the optical signals around and between circuit boards can addsignificant additional complexity. Marketable optical interconnectsbetween chips have therefore proven elusive, despite the need forbroadband data transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a layer of an optical crossbar switch inaccordance with examples of the present disclosure;

FIG. 2 is a schematic view of stacked layers in an optical crossbarswitch in accordance with examples of the present disclosure;

FIG. 3 is a three-dimensional schematic view of stacked optical crossbarswitch layers in accordance with examples of the present disclosure;

FIG. 4 includes block diagrams of micro-electro-mechanical systemactuated optical devices in accordance with examples of the presentdisclosure;

FIG. 5 is a block diagram of an optical device including multipleindependently movable portions in accordance with examples of thepresent disclosure;

FIG. 6 is a block diagram of an intersection of a waveguide in a layerof an optical switch fabric with an interlayer waveguide in accordancewith examples of the present disclosure;

FIG. 7 is a block diagram of stacked waveguide layers and an opticalpath through the layers in accordance with examples of the presentdisclosure;

FIG. 8 is a block diagram of an optical-electrical-optical conversiondevice in a waveguide in accordance with examples of the presentdisclosure; and

FIG. 9 is a flow diagram of a method for switching a circuit switchedoptical device in accordance with examples of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made to the examples illustrated, and specificlanguage will be used herein to describe the same. It will neverthelessbe understood that no limitation of the scope of the technology isthereby intended. Additional features and advantages of the technologywill be apparent from the detailed description which follows, taken inconjunction with the accompanying drawings, which together illustrate,by way of example, features of the technology.

Light beams or optical signals are frequently used to transmit digitaldata. For example, optical signals can be used to transmit data overlarge distances, between electronic components on nearby circuit boards,or between electronic components on a single circuit board. For largescale interconnections between multiple electronic components, anoptical fabric can be used which can have a number of characteristics,including the ability to connect any or all of the inputs to any or allof the outputs with a minimal number of components. An optical fabriccan also have a high coupling efficiency, modularity, high reliability,an ability to reroute a workload to eliminate system congestion, and lowcost.

Optical signals can be routed using waveguides. Waveguides can carryoptical energy by imposing boundaries which control the expansion of theoptical energy and guide the optical energy or optical signals to adesired location. Optical communication can also provide interconnectionbetween the optical channel and various other devices such asbackplanes, electronic devices, semiconductor lasers, photo-detectors,other components. An optical interconnect between waveguides withoptical switches have a high coupling efficiency, low cost,reconfigurability, and can produce a reliable connection.

A hollow waveguide, such as a hollow metal waveguide, can be efficientlyand inexpensively used in a circuit switched optical crossbar fabric.Hollow metal waveguides typically include a hollow air core surroundedby highly reflective metallic wall. Hollow metal waveguides aretypically fabricated in any of a variety of substrates, includingsilicon. A variety of patterning processes including sawing, lasermachining, wet and dry etching, and other suitable processes can be usedto form the hollow metal waveguides. For example, some forms of plasticmolding are used to create trenches which can be metalized to formhollow metal waveguides. According to a more specific example, thesidewalls and bottom of these trenches are metalized using a sputteringprocess to provide a highly reflective surface at the wavelengths ofinterest. Silver can be sputter-coated into the trenches to provide thereflective coating. The silver can be overcoated with a passivationlayer, such as aluminum nitride, which can protect the coating andprevent oxidization. An undercoat may also be provided to improve theadhesion of the silver layer to the substrate. A waveguide cap can alsobe bonded or patterned on the substrate to cover the trenches andcomplete the hollow metal waveguides. Typical dimensions of a hollowmetal waveguide cross-section may be approximately 150 microns×150microns or 300 microns×300 microns, for example. That being stated, thesize and geometry of the waveguides can be altered according to thespecific design for single or multimode optical properties.

Low index air cores of the hollow metal waveguides produce variouseffects not found in polymer core waveguides. Hollow metal waveguidesoffer the potential of low optical loss, low bend loss, and low modaldispersion required in optical interconnect systems. In contrast topolymer or other solid waveguides, the hollow metal waveguides do nothave reflective losses at the input and output facets. In fact, somesilver-coated hollow metal waveguides fabricated in silicon haveachieved losses lower than 0.05 dB/cm. Air cores of the hollow metalwaveguides produce very little optical dispersion, which allows thehollow metal waveguides to transmit data at rates approaching terahertzfrequencies.

With this in mind, a circuit switched optical device in accordance withan example of the present technology includes a first array ofintersecting hollow waveguides formed in a first plane of a substrate. Asecond array of intersecting hollow waveguides is formed in a secondplane of the substrate, and the second plane is typically parallel tothe first plane. An optical element within the first array selectivelyredirects an optical signal from the first array to the second array.

Alternatively, a method for switching a circuit switched optical deviceis also disclosed and will be discussed in greater detail hereinafter.That being said, it is noted that when discussing circuit switchedoptical device or the method of switching the same, each of thesediscussions can be considered applicable to each of these examples,whether or not they are explicitly discussed in the context of thatexample. Thus, for example, in discussing details about the circuitswitched optical device per se, or the method, such discussion alsorefers to the other example, and vice versa.

That being stated, computers and other devices can be opticallyconnected and optically switched using the circuit switched opticaldevice. For example, the circuit switched optical device can opticallycouple backplanes, blades, and other devices in a server. As usedherein, it is noted that the term “backplane” refers to a structurewhich has multiple communication channels which can be accessed througha number of integrated sockets or other receptacles. For example, abackplane may contain a common bus to which a number of separate devicesmay connect. Backplane communication channels may include electricalwires, optical fibers, hollow metal waveguides, or other channels. Thebackplane may contain optical to electrical transducers, signalprocessing electronics, various types of light sources. Where the term“optical backplane” is used, the backplane includes at least one channelwhich is configured to convey optical signals through the backplane.

An optical interconnection fabric according to an example of the presentdisclosure includes dynamically reconfigurable circuit switched opticalcrossbars which allow X input nodes to connect to any of Y output nodesacross Z layers of waveguide arrays. The values of X, Y, and Z arelimited only by space and desired complexity. That being said, in onespecific example, X and Y can independently be from 2 to thousands (oreven more), and Y can be from 2 to hundreds (or even more), though thesenumbers are not intended to be limiting. The optical crossbars can becreated using a low cost injection molding processes. A number ofcrosspoints or intersections can route optical signals from the inputnodes to the output nodes. The crosspoints can be implemented in avariety of ways, including mechanical actuators or multicasting to alloutputs and controlling the connections using light valves. Crosspointscan switch an input to a desired output in a matter of tens ofmilliseconds, tens of microseconds, or less.

Turning now to the FIGs., FIG. 1 is schematic diagram of a circuitswitched optical crossbar fabric 100 which connects four bus ports tofour input/outputs (I/O) ports. A number of horizontal linesrepresenting waveguides run from left to right and intersect each of anumber of vertical lines, also representing waveguides. Each of thevertical lines connects to one of the input/output ports. Forconvenience, the horizontal lines can be called “bus lines” 110 and thevertical lines can be called “tap lines” 115. As used herein, the term“crossbar” or “crossbar configuration” refers to two or more opticalpaths which intersect. The intersection of the bus lines and the taplines create an optical crossbar fabric. In one example, the bus linescan be formed in an array of parallel waveguides which intersect the taplines at approximately a 90 degree angle, though other angles can beused in other examples.

The bus lines 110, numbered 1′-4′, can carry input and output signalsthrough the optical fabric. The tap lines 115, numbered 1-4, can beselectively connected to the bus lines to connect a bus port to an I/Oport. A computational element, such as a computer, router, electronicswitch or other device with E/O or O/E (electrical to optical, opticalto electrical signal converters) can be connected to the input/outputport(s) which can be optical signal in and optical signal out ports.

The bus lines 110 and tap lines 115 may be hollow metal waveguides. Ateach intersection between the bus and tap lines, an optical element 120can be selectively actuated to direct optical energy between theintersecting lines. By configuring an optical crossbar fabric at theintersections in this manner, each of the signals carried by in a busline can be directed to any of the outputs.

A crosspoint or optical switch can have at least two configurations: athrough state and a crossed state. In a through state, bus lines cancarry signals through an optical fabric. For example, the bus lines cancarry bidirectional signal traffic by dividing the lines into twogroups. Similarly, the tap lines can be divided into groups forbidirectional signal traffic. Bus lines in the through state can passthrough the optical switch without diversion into the tap lines. Thesignal carried by the bus lines can then be received by anothercomponent connected at another location along the bus lines.

In a crossed state, the optical switch can diverts the bus lines intothe tap lines. A component attached to the tap lines can establishbidirectional communication with devices through the bus lines and taplines. The optical switch may have a variety of configurations and use anumber of technologies to redirect optical signals to the tap lines.

For purposes of illustration and explanation, a relatively small numberof bus lines and tap lines have been illustrated. The optical switchcould have fewer or greater numbers of lines, according to specificsystems and applications.

Referring to FIG. 2, the optical crossbar fabric can be substantiallyduplicated in another layer which can be stacked on top of the opticalcrossbar fabric described in FIG. 1. Any desired number of layers ofoptical crossbar fabrics can be stacked to provide an optical switch forswitching optical signals between any desired numbers of devices.Stacking layers of optical crossbar fabrics in this manner can enable amore densely organized switching fabric with a smaller footprint than ifa same number of ports were organized within a single layer. Forexample, a switch may service a grid of 1000×1000 ports. Arranging theswitching fabric in a cube rather than a plane can result in a morecompact switch.

The use of individual optical devices in the intersections between busand tap lines can result in very fast switching times between thethrough and crossed states. A low mass of the optical devices can allowfor fast motion with minimal power. Further, in examples where theoptical devices are individually actuated, the optical switch canprovide increased flexibility in routing the optical signals. Forexample, in applications where signal throughput to a computing deviceattached to the tap lines is not a deciding factor, only a few of buslines may be diverted into the tap lines. The remainder of the bus linescan then be used to carry other traffic. Optical devices used fordirecting an optical beam between layers can be placed at theintersections or outside of the intersections. In examples where eachintersection includes an optical device for optical routing within alayer, optical devices for interlayer redirection can be placed at eachof the tap lines or each of the bus lines, in each of the intersections,etc. In another example, a single optical device for interlayerredirection may be provided for each layer and the optical devices atthe intersections can be used to redirect an optical beam to theinterlayer redirection optical device, and from there to a desired port.

FIG. 2 is diagram of stacked circuit switched optical crossbar fabrics200 which can separately connect four bus ports to four input/outputsports or together can connect eight bus ports, numbered 1′-8′, to eightinput/output ports, numbered 1-8. Each optical crossbar fabric layer canoperate separately and independently in the manner as has beendescribed. A first waveguide layer can include bus lines 210, tap lines215, and optical devices 220 in intersections of the bus and tap lines.A second waveguide layer can include separate bus lines 225, tap lines230, and optical devices 235.

An interlayer waveguide 240 can also be included between the opticalcrossbar fabric layers to facilitate transmission of a signal from onelayer to another layer. The interlayer waveguide can be formed similarlyto the waveguide arrays in the single layer array described in FIG. 1.Where sidewalls of the waveguides in the waveguide arrays are metallizedto keep the optical signal within the waveguide, the interlayerwaveguide can be at a point of non-metallization to enable the opticalsignal to travel out of the waveguide at a direction orthogonal to aplane of the waveguide array. The length of the interlayer waveguide canbe the thickness between stacked waveguides. Thus, for example, if ametallization layer is all that separates stacked waveguides, theinterlayer waveguide length may be minimal, or even negligible. In thisexample, the interlayer waveguide may simply comprise the passagewayfrom one waveguide layer to another waveguide layer. In other examples,a layer having a measurable or significant thickness may exist betweenstacked waveguide arrays. In this example, sidewalls of the interlayerwaveguide can be metallized such that an optical beam will be directedalong the interlayer waveguide as with other waveguides in the waveguidelayers.

An optical signal can be directed along the interlayer waveguide usingan optical element. The optical element for directing an optical signalbetween layers can be the same optical element as is used in theintersections to direct a signal from a bus port to an I/O port, or canbe an optical element set outside of an intersection. For example, FIG.2 illustrates optical elements at the waveguide array intersections andseparate optical elements outside of the intersections for direction anoptical beam from one layer to another layer.

Referring to FIG. 3, a three-dimensional schematic view is shown ofstacked optical crossbar switch layers 300 in accordance with anexample. Bus lines 310 and tap lines 315 are arranged in grid patternsin the layers, and interlayer waveguides 320 intersect the bus linesoutside of an intersection near an end of the bus lines. In a relatedexample, a three-dimensional schematic view can include stacked opticalcrossbar switch layers that are present at every intersection, ratherthan just at single end of a bus line or a tap line. In another example,a multi-layer grid or cube of waveguides includes only a singleinterlayer waveguide for connecting all of the layers.

The interlayer optical element and/or the optical elements at theintersections may comprise micro-electro-mechanical system (MEMS)devices. The MEMS devices can be positioned in a substrate beneath,above, or to the side of a waveguide wall. The MEMS devices can includea mirror, a polarizer, a prism, a lens, or other type of optical devicefor directing or conditioning an optical beam. The MEMS devices caninclude an actuator for moving the optical elements. The actuator can beconfigured to switch or move an attached optical element betweenpositions in approximately 20 ms (milliseconds) or less.

As illustrated in FIG. 4, the MEMS device can have a variety ofconfigurations. In example (A), the MEMS device includes a mirror 410hingedly mounted on an edge of the mirror near a wall of a waveguide405. The mirror can swing upward or downward at the hinge using anactuator 415 to move into and out of a path of an optical beam. When themirror is moved out of a path of the optical beam, the mirror can besubstantially flush with a sidewall of the waveguide such thattransmission of the optical beam past the mirror is not inhibited. Inone example, two such MEMS actuated mirrors can be used to direct alight beam from one waveguide to another, turning the light beampropagation direction by 90 degrees. In example (B), the MEMS deviceincludes a mirror or reflective block 420 which is moved upward anddownward using an actuator 425 to move into and out of the pathway ofthe optical beam. In other configurations, a mirror or other opticaldevice can be positioned in a number of different positions. Thus, theMEMS device can move the mirror in one position to redirect an opticalbeam along a different waveguide in a same waveguide layer, and can movethe mirror into another position to redirect the optical beam to adifferent waveguide layer. The MEMS device can also move the mirror outof the waveguide path to not redirect the optical beam. In anotherexample, multiple MEMS devices can be included at a single waveguideintersection, where one device redirects an optical beam within the samewaveguide layer and another device redirects the optical beam to adifferent waveguide layer.

The optical device can have a variety of different characteristicsdepending on a particular application. For example, the optical devicecan include a partially reflective film or plate. As another example,the optical device can include a beam splitter. The beam splitter can bea generic or 50-50 (or any other ratio) beam splitter which splits theoptical beam and redirects approximately one half of the optical beamwhile transmitting another approximately one half of the optical beamwithout redirection. As another example, the beam splitter can be adichroic beam splitter to transmit a portion of the optical beam at afirst wavelength and redirect a portion of the optical beam at a secondwavelength. The beam splitter can be a dielectric beam splitter or acube beam splitter. The beam splitter can be a polarizing beam splitteror a wire grid polarizing beam splitter and can split an optical beamaccording to polarization.

The optical device can have a width or height substantially similar to awidth or height of a waveguide in which the optical device is disposed.In another example, the optical device can have a width or height lessthan the width or height of the waveguide in which the optical device isdisposed. For example, the optical device can have a width half as wideas a width of the waveguide. Thus, the optical device may only affect aportion of the optical beam which is incident on the optical device.

The optical device can be a mirror for reflecting and/or redirecting anoptical beam. In one example, the mirror can be made of multiple parts.For example, as shown in FIG. 5, the mirror may include two mirrorhalves or portions 510, 515. The mirror halves can be independentlymovable. The mirror portions can be independently movable using a sameMEMS device or may be operated using multiple MEMS devices. For example,one mirror portion may be extended into the waveguide into a path of anoptical beam while another mirror portion is positioned partially orentirely out of the path of the optical beam. The mirror portions can bemade to interlock or fit together within a waveguide or waveguideintersection.

The use of beam splitters, mirrors that extend only partially into awaveguide, MEMS devices which can selectively determine an extent towhich an optical device extends into a waveguide, and so forth, can beused for multicasting or broadcasting an optical signal. Also, the useof dichroic or polarizing optical devices can enable monitoring of awavelength or polarization of the optical signal.

Any of the described variations in optical device configurations can beused at any of the intersections and/or for interlayer communication.Thus, for example, an optical beam from a bus line may be split at anintersection using a 50-50 beam splitter such that half of the opticalsignal is redirected along a tap line and the other half continues alongthe bus line. The half that continues along a bus line may thenencounter a dichroic beam splitter that redirects green light within theoptical beam to a different layer and transmits red light along the busline. FIG. 6 illustrates an example configuration where an optical beam605 transmitted along a waveguide bus or tap line 610 is split using abeam splitter 630 and a portion 620 of the optical beam is redirectedalong an interlayer waveguide 615. Another portion 625 of the opticalbeam is transmitted along the tap line. The light directed to adifferent layer can be redirected into a bus line or a tap line. Thewaveguide arrays at different layers can be aligned, offset, skewed,etc., as desired and the interlayer waveguide can connect waveguides indifferent layers. The optical devices can be rotated or positioned suchthat the optical beam can be efficiently and accurately redirectedbetween the switching fabric layers. Also, the waveguide arrays can bearranged in regular or grid-like patterns or can be arranged inirregular patterns.

Referring to FIG. 7, an optical switch is made up of a first or bottomwaveguide layer 710, a second waveguide layer 720, and a third or topwaveguide layer 740, with a spacer layer 730 interposed between thesecond and third waveguide layers. The optical switch can be placed in asocket in a backplane. A number of hollow metal waveguides are formed inthe backplane and intersect the socket. The optical switch can beconfigured to receive optical energy passing through the hollow metalwaveguides and route the optical energy appropriately. An optical signal705 can be received in a waveguide in the first waveguide layer throughthe socket and from a waveguide in the backplane. An optical device 715can redirect the optical beam to the second layer where an opticaldevice 724 in the second layer redirects the optical beam along awaveguide in the second layer. Another optical device 728 in the secondlayer can then redirect the optical beam up through the spacer layer tothe third or top layer where an optical device 745 in the third layerredirects the optical beam within a waveguide in the third layer. Theoptical beam can then be transmitted to a device connected to a port inthe third layer. In another example, the optical beam in the third layercan be transmitted back to the backplane to a different waveguide thanthe original optical beam.

In another example, the spacer layer can be a waveguide layer similarlyto the first, second, and third layers. An optical device in the spacerlayer can be positioned out of the path of the optical beam between thesecond and third layers such that the optical device in the spacer layerhas no effect on the optical beam passing through the spacer layer. Inanother example, the optical beam path illustrated in FIG. 7 can proceeddirectly from the first layer to the third layer without interactionwith the second layer.

In one example, the layers of waveguides can have cross sections whichare approximately 150 microns×150 microns. The center to center distancebetween two stacked waveguides can be approximately 250 microns.

In another example, each of the tap lines may contain a light valve. Thelight valves can selectively block or transmit optical signals throughthe tap lines. By controlling the transmission of optical signal throughthe tap lines, the light valves can configure the optical fabric tointerconnect specific elements attached to the fabric. A number of busports or light sources can be attached to each bus line. As beams fromthe light sources are diverted into the tap lines, the beams canencounter the light valves. If the light valve for a particularinput/output port is open, the light can be transmitted out through theport. Use of light valves can be valuable, for example, whenbroadcasting a signal to a large number of ports, but not to all ports.

One challenge in designing an optical crossbar fabric is budgeting andreducing optical losses that are experienced by an optical signaltraveling through the system. Each time the optical signal encounters anobstacle or discontinuity in its path, a portion of the light may belost due to absorption and/or scattering. In general, the more elementsthe optical signal encounters, the higher the losses within the fabric.Further, certain types of elements can introduce greater losses thanother elements. Consequently, to reduce the optical losses an overallnumber of elements optical signal encounters within the optical fabriccan be reduced and the use of each element can be weighed against thebenefit provided.

Referring to FIG. 8, an optical-electrical-optical (OEO) device isillustrated for restoring an optical signal. The OEO device can be sizedand shaped to be implemented within a hollow metal waveguide 805. As aweak signal 810 approaches the OEO device from the right, a lens 815 canbe used to collimate the light and focus the light to a photodetector820. The photodetector can generate an electrical signal based on thelight received. An application specific integrated circuit (ASIC) chip825 can condition the electrical signal generated by the photodetector.For example, the ASIC can increase a strength of the electrical signaland/or remove noise from the electrical signal. The ASIC can send theconditioned electrical signal to a vertical-cavity surface-emittinglaser (VCSEL) 830 or other suitable light source. The VCSEL can emit orbroadcast a restored optical signal 840. The OEO device can also includeanother lens 835 for collimating or shaping the restored optical signalfor transmission along the waveguide to the left.

An optical switch can include any number of OEO devices. For example, anOEO device may be provided in each waveguide layer. As another example,a single OEO device may be provided for an entire optical switch. Theoptical switch can include logic circuitry or be in communication with amemory and/or processor to be able to determine when an optical path foran optical signal will weaken the optical signal sufficiently that useof the OEO device on the signal will be useful for providing asufficient output signal. For example, when an optical path isparticularly long, includes more than a predetermined number of turns,or encounters specific optical devices or other features which are knownto cause signal loss, the optical switch can reroute the optical path topass through the OEO device before reaching the destination. In anotherexample, optical detectors can be included in the waveguides to detectoptical signal strength. When the signal strength drops below apredetermined strength, the switch can dynamically reroute the opticalbeam to a nearest OEO before the optical beam reaches the destination.

Measurements and modeling have shown that losses at individualintersections can be comparatively minimal. For example, where in inputbeam is directly transmitted to an output, or transmitted with only oneor two turns, an exiting beam may have approximately 99% or more of theintensity of the input beam. However, in designs where the opticalsignal encounters large numbers of intersections the loss can besignificant. For example, in an optical fabric having 32 tap lines foreach computing element, if 16 computing elements are interconnectedusing the optical fabric, then a given line may encounter as many as 512intersections. Using a worst case scenario, a magnitude of the exitingoptical signal beam after encountering 512 intersections may be onlyabout 2% of the original input magnitude. At some point along the pathamong the 512 intersections, the optical beam can be directed to an OEOdevice and strengthened such that the exiting optical beam has a signalstrength within a predetermined range from the original signal strength.For example, the optical switch can be designed to ensure that allexiting optical beams have a signal strength of at least 25% or 50% ofthe original signal strength. A minimally acceptable signal strength maybe determined based on a specific application or system configuration.

The OEO can be formed separately from the circuit switched opticaldevice or as a part of the circuit switched optical device. For example,if the OEO is separate from the circuit switched optical device, anoptical fiber can carry light from a waveguide to the OEO forconditioning and another optical fiber can carry the conditioned lightfrom the OEO to the same or a different waveguide. As another example,the OEO can be formed separately from the circuit switched opticaldevice and inserted into the waveguide. As another example, the OEO canbe formed integrally with the circuit switched optical device in awaveguide of the circuit switched optical device such that the OEO andthe circuit switched optical device can be a single integrated device.By positioning an integrally or separately formed OEO in the waveguide,an additional expense of attaching optical fibers to the waveguide(s)and the OEO can be eliminated.

The optical crossbar fabrics described above can be used in a variety ofapplications. For example, a computer system which includes a number ofblade computers can be connected to the optical crossbar fabric. Theoptical crossbar fabric can include a number input/output portsconnected to bus lines. The tap lines can be connected to the bus linesat intersections. Different layers of waveguides can be connected todifferent blade computers, and bus and/or tap lines in one layer can bein optical communication with bus and/or tap lines in another layer. Thetap lines can be connected to the blades. For example, the blades can beconnected to the tap lines through a PCI-E (Peripheral ComponentInterconnect Express) connector with 16 transmit lines and 16 receivelines, for a total of 32 lines per blade.

FIG. 9 is a flow diagram of a method 900 for switching a circuitswitched optical device in accordance with an example of the presentdisclosure. The method can include determining 910 an optical beam pathfrom an input port in a first hollow waveguide layer to an output portin a second hollow waveguide layer. The optical path can also be splitto include destinations in both the first and second hollow waveguidelayer. The first and second hollow waveguide layer can be adjacentlayers or have any number of layers interposed therebetween.

The method can also include moving 920 an optical element in a firstarray of intersecting hollow waveguides in the first hollow waveguidelayer to redirect an optical beam from the first array of intersectinghollow waveguides to a second array of intersecting hollow waveguides inthe second hollow waveguide layer. The method can also include moving anoptical element in the second array to redirect the optical beam along awaveguide in the second array. The method can further include moving anynumber of other optical elements within the first and second arrays toselectively direct the optical beam along a desired path within thefirst and second hollow waveguide layers.

An additional step includes transmitting 930 the optical beam from theinput port through first array of intersecting hollow waveguides in thefirst hollow waveguide layer. The optical beam can be redirected 940 tothe second array of intersecting hollow waveguides using the opticalelement, and the optical beam can be directed 950 along the second arrayof intersecting hollow waveguides in the second hollow waveguide layertoward the output port.

The method can also include conditioning the optical beam using anoptical-electrical-optical (OEO) device. For example, conditioning caninclude collimating the optical beam to efficiently launch the opticalbeam into the hollow waveguide. More specifically, the collimation ofthe optical beam can reduce a divergence angle of the optical beam so asto substantially match an acceptance angle for low loss propagation intohollow metal waveguides. In this example, a lens and source (or an arrayof lenses and sources) in the OEO can be internal or external to thehollow waveguide(s). Likewise, a second lens and a detector in the OEOcan also be internal or external to the hollow waveguide(s).

In another example, conditioning the optical beam may compriseregenerating the optical signal (i.e., the optical beam) if the opticalsignal is too weak, such as by having a signal strength lower than apredetermined threshold.

The method can also include redirecting a portion of the optical beamand transmitting another portion of the optical beam. For example, theoptical element may comprise a mirror having a plurality of mirrorportions and the method may proceed by moving the plurality of mirrorportions independently to selectively redirect a portion of the opticalbeam.

The method can also include moving an array of optical elements withinthe first hollow waveguide layer and the second hollow waveguide layerto direct a plurality of optical beams between input and output portscoupled to intersecting arrays of hollow waveguides in the first hollowwaveguide layer and the second hollow waveguide layer.

The device and method described herein can be further described inaccordance with a specific example. For example, the device and methodcan include a circuit switched optical crossbar fabric, which is formedwith hollow metal waveguides at a first layer in a backplane to createan optical crossbar architecture. A first group of parallel crossbarsmay be bus lines which traverse the length of the backplane, while asecond group of parallel crossbars may be tap lines which intersect thebus lines and are connected to a computing element. Additionally, anoptical element or combination of optical elements in each intersectionin the first layer can be configured to selectively direct opticalsignals from the bus lines into the tap lines and vice versa. Theseoptical elements may include prisms, mirrors, light valves and otheroptical elements. The optical elements may be dynamic or passive.According to one illustrative example, one or more optical element inthe intersection can change states to switch the interconnection from athrough state to a crossed state. Further, hollow metal waveguides canbe formed in a second layer in proximity to the first layer, and thefirst and second layers can be directly adjacent or may have any numberof intervening layers. An optical element or combination of opticalelements can be positioned to selectively direct optical signals fromthe bus lines into the tap lines and vice versa. Computing elements canbe connected to the optical fabric. For example, a primary computingdevice or network may be connected to the bus lines and a number ofother computing devices may be connected to the tap lines. Also, the buslines may be connected to a larger computing network or router and thetap lines may be connected to a number of blade computers. Each of theblade computers may be connected to multiple tap lines. For example,each blade computer may use 16 tap lines for inbound communication and16 tap lines for outbound communication. In other examples, thecomputing devices may use more or less tap lines for bidirectionalcommunication. The computing device may also use, for example, 16 taplines in a bidirectional manner. Additionally, the computing device mayuse wavelength division multiplexing for bidirectional communicationover a given line set.

As discussed above, the bus ports may be connected in a variety oflocations along the bus lines. In some examples, it may be advantageousto locate the bus ports at one end of the bus lines. In other examples,bus ports may be attached to the center of the bus lines and distributeoptical signals in both directions through the bus lines. In general,the location of the bus ports on the bus lines can be determined by anumber of factors including: space constraints, connection constraints,optical loss budgeting, or other relevant criteria.

Dynamically switching the optical elements within the crossbar opticalfabric to connect desired tap lines to the bus lines can be carried outin some examples. For example, dynamically switching the opticalelements may include separately switching a number individual elementsor moving a block of elements with a single actuator. By way of exampleand not limitation, this switching may include moving a solid periscopeprism into the path of a bus line, tilting mirror into the path of a busline, or opening a light valve to allow passage of optical signals froma bus line into a tap line.

Furthermore, the optical signals from the tap lines can be directed tothe computing element. In one example, the optical signal from multipletap lines may be combined into a single tap line using a series ofcombiner elements. Additionally or alternatively, a single tap line maybe simultaneously connected to two or more bus lines.

In sum, the optical interconnect fabric described above provides anumber of advantages including: low cost, non-blocking configuration,low power, multicast capability and fast switching. The opticalinterconnect fabric can also connect a large number of devices in a morecompact area by providing optical interconnection between layers ofwaveguides in the optical interconnect fabric. The various examples inthe present disclosure are not mutually exclusive. Additionally, thevarious optical elements can be used separately, in conjunction witheach other, or can be substituted for each other.

While the forgoing examples are illustrative of the principles of thepresent technology in particular applications, it will be apparent tothose of ordinary skill in the art that numerous modifications in form,usage and details of implementation can be made without the exercise ofinventive faculty, and without departing from the principles andconcepts of the technology. Accordingly, it is not intended that thetechnology be limited, except as by the claims set forth below.

What is claimed is:
 1. A circuit switchable optical device, comprising:a first array of intersecting hollow waveguides formed in a first planeof a substrate; a second array of intersecting hollow waveguides formedin a second plane of the substrate, wherein the second plane is parallelto the first plane; and an optical element within the first array toselectively redirect an optical signal from the first array to thesecond array; wherein the optical element includes two or moreindependently movable portions.
 2. The device of claim 1, wherein thefirst array of intersecting hollow waveguides and the second array ofintersecting hollow waveguides comprise hollow metal waveguides.
 3. Thedevice of claim 1, wherein the first array of intersecting hollowwaveguides comprises a plurality of hollow waveguides intersecting at anintersection and wherein the optical element is positioned at theintersection.
 4. The device of claim 1, wherein the first array ofintersecting hollow waveguides comprises a plurality of hollowwaveguides intersecting at an intersection and wherein the opticalelement is positioned outside of the intersection.
 5. The device ofclaim 1, wherein the optical element comprises amicro-electro-mechanical system.
 6. The device of claim 1, wherein theoptical element comprises a mirror.
 7. The device of claim 1, whereinthe optical element comprises a beam splitter.
 8. The device of claim 1,wherein the optical element comprises two mirror portions.
 9. The deviceof claim 1, further comprising: an optical-electrical-optical device toconvert to electrical signal, amplify, and retransmit the opticalsignal.
 10. A method for switching a circuit switched optical device,comprising: determining an optical beam path from an input port in afirst hollow waveguide layer to an output port in a second hollowwaveguide layer; moving an optical element in a first array ofintersecting hollow waveguides in the first hollow waveguide layer toredirect an optical beam from the first array of intersecting hollowwaveguides to a second array of intersecting hollow waveguides in thesecond hollow waveguide layer; transmitting the optical beam from theinput port through first array of intersecting hollow waveguides in thefirst hollow waveguide layer; redirecting the optical beam to the secondarray of intersecting hollow waveguides using the optical element; anddirecting the optical beam along the second array of intersecting hollowwaveguides in the second hollow waveguide layer toward the output port,wherein the optical element comprises a mirror having a plurality ofmirror portions, the method further comprising moving the plurality ofmirror portions independently to selectively redirect a portion of theoptical beam.
 11. The method of claim 10, further comprisingconditioning the optical beam using an optical-electrical-opticaldevice.
 12. The method of claim 10, wherein redirecting the optical beamcomprises redirecting a portion of the optical beam and transmittinganother portion of the optical beam.
 13. The method of claim 10, furthercomprising moving an array of optical elements within the first hollowwaveguide layer and the second hollow waveguide layer to direct aplurality of optical beams between input and output ports coupled tointersecting arrays of hollow waveguides in the first hollow waveguidelayer and the second hollow waveguide layer.
 14. The method of claim 10,wherein the optical beam is directed through anoptical-electrical-optical device to convert to electrical signal,amplify, and retransmit the optical signal.